1. Homeostasis and Cellular Maintenance
Homeostasis is the process by which biological systems maintain a stable internal environment despite external changes. Cells maintain homeostasis through:
Selective permeability of the cell membrane: Controls what enters and exits.
Active and passive transport: Uses diffusion, osmosis, and active transport.
Enzyme regulation: Helps maintain metabolic balance.
Feedback mechanisms: Such as negative feedback loops.
2. Diagram Analysis
2.1 Active Transport Identification
The figure representing active transport is likely C because:
It requires energy (ATP).
It moves substances against their concentration gradient.
2.2 Facilitated Diffusion
The figure showing facilitated diffusion is likely B because:
It moves molecules down their concentration gradient with the help of a protein.
2.3 Process in A
The process in A is simple diffusion.
To indicate equilibrium, we modify A by showing equal concentration of molecules on both sides.
2.4 What Drives A and B?
A (Simple diffusion): Driven by the concentration gradient.
B (Facilitated diffusion): Driven by the concentration gradient but requires a transport protein.
3. Transport of Ions
3.1 Hydrogen Ion Transport
Active transport moves H+ ions from the cytoplasm to the extracellular fluid.
3.2 Limiting Factor for Sucrose Transport
The availability of H+ ions and carrier proteins.
3.3 Increasing Sucrose Transport Rate
Increase H+ ion concentration.
Increase carrier proteins.
Increase ATP availability.
4. Effect of Reversed Na+/K+ Antiporter
If the Na+/K+ antiporter is inserted in reverse, sodium and potassium movement will be disrupted.
This will reduce Na+ movement into the cell, preventing the glucose/Na+ symporter from functioning properly, reducing glucose transport.
5. Osmosis and Diffusion
5.1 Glucose Concentration on Side B at Equilibrium
Glucose will move freely across the membrane until its concentration is equal on both sides.
5.2 Which Side Has More Water?
The side with lower solute concentration will have more water.
5.3 If Membrane is Permeable to Water, Glucose, and Sucrose?
Water will be evenly distributed since all solutes can move freely.
5.4 Passive Movement of Solvent Across Membrane
Osmosis.
5.5 Passive Movement of Solutes Across Membrane
Diffusion.
5.6 Conditions for Equilibrium in Plant Cells
Isotonic solution (equal solute concentration inside and outside).
Turgor pressure (water balance inside the vacuole).
5.7 More Water If Sucrose Increases to 1.0M?
Side A will have more water because sucrose creates a higher osmotic pressure on Side B.
5.8 If Membrane is Only Permeable to Water?
Side B will have more water.
Sucrose and glucose concentrations on Side A will increase.
6. Types of Endocytosis
Receptor-mediated endocytosis: Specific molecules bind to receptors before being engulfed.
Pinocytosis: "Cell drinking" – the cell engulfs fluids.
Phagocytosis: "Cell eating" – the cell engulfs large particles.i
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